The first step in the treatment of waste water is the removal of coarse solids, such as chunks of hard soil, in order to prevent these solids from damaging piping or other equipment further on in the treatment process. The removal of solids is for example effected by placing screens in the waste water stream to be treated, or by installing cloth filters. Another method of removing these solids is by feeding the waste water into a so-called internally fed drum filter.
The use of internally fed drum filters for separating solid substances from fluids is known from for example U.S. Pat. No. 3,275,150, which describes a rotary drum filter for the thickening of e.g. fluids as used in the manufacturing of paper. The described apparatus comprises a drum revolving in a tank containing e.g. paper pulp stock. The fluid is drained away and thickened paper slurry is processed further to produce paper. When treating waste water the opposite is true, i.e. that the fluid is processed further whereas the solid substances are removed.
Another internally fed drum filter is known from WO2011161327. This publication describes a process for treating waste water comprising organic material, such as waste water originating from a food industry plant, wherein waste water is led through a first purification phase comprising a drum screen, for separating the coarsest solid debris from the waste water.
An internally fed drum filter generally comprises a water-permeable drum that is rotatable in a casing and an inlet duct that discharges e.g. waste water inside the drum filter. The inner surface of the drum filter is provided with a spiral that due to rotation of the drum enables solid substances present in the waste water to be pushed towards the end of the drum filter opposing the inlet duct end in order to be removed. At the same time the permeability of the drum enables water to leave the drum filter via the circular drum wall for receiving further treatment.
However, a disadvantage is that the inlet areas of these drum filters are prone to clogging. Therefore, it has been proposed in the prior art to incorporate an inlet distributor into the filter design. These inlet distributors are generally of the “headbox” type. A headbox is a type of shallow water reservoir connected to the inlet pipe, that allows waste water to flow over the edges of the reservoir, whereas the solid substances remain in the reservoir to be discharged evenly to the drum filter via the bottom of the reservoir.
These headbox type inlet distributors have several disadvantages. A first disadvantage is that debris may build up inside the reservoir, causing the headbox itself to clog. Another disadvantage is that foul water may be retained in the reservoir, especially during low supply rates of waste water via the inlet duct, causing fouling of the reservoir and causing it to generate a rather unpleasant smell. A further disadvantage is that the flow characteristics of the flow of waste water entering the drum filter via the inlet duct can not be adjusted, e.g. the flow velocity of the incoming waste water can not be regulated in any way.
Therefore, it is an object of the invention to provide an inlet distribution arrangement for an internally fed drum filter, wherein the flow characteristics of the waste water entering the drum filter via the inlet duct can be adjusted.